1. Field of the Invention
The present invention relates to a liquid ejection apparatus and a liquid restoration method, and more particularly, to a liquid ejection apparatus and a liquid restoration method whereby the amount of dissolved gas in the liquid can be controlled and the liquid can be maintained in a desirable state.
2. Description of the Related Art
In recent years, inkjet printers have become widespread. An inkjet printer forms an image on an ejection receiving medium, such as paper, by ejecting ink from nozzles onto the ejection receiving medium. Furthermore, inkjet heads are known as ejection devices for ejecting ink, and such inkjet heads include, for example, an inkjet head which uses a so-called piezoelectric type of actuator for applying a pressure wave to ink inside a pressure chamber connected to a nozzle, an inkjet head which uses a so-called thermal jet type of actuator for generating a bubble by heating ink inside the pressure chamber, and the like. Ink is ejected from nozzles by operating ejection devices described above, thereby forming an image on the ejection receiving medium.
In an inkjet printer of this kind, if an undesired air bubble is generated unintentionally in the ink inside the inkjet head, then there is a loss in the pressure applied by the actuator to the ink, and ejection abnormalities such as ink ejection volume abnormalities, ejection direction abnormalities, ejection failures, and the like, may occur. Ejection abnormalities of this kind cause a marked decline in image quality.
Japanese Patent Application Publication No. 2000-190529 discloses a method in which the amount of gas dissolved in liquid that has been expelled without being ejected from the inkjet head is measured, and the amount of dissolved gas in the liquid inside the inkjet head is controlled in such a manner that the measured amount of dissolved gas in the liquid in the inkjet head becomes equal to or less than a prescribed value. More specifically, if the measured value of the amount of dissolved gas in the liquid expelled from the inkjet head exceeds the prescribed value, then the supply of liquid to the inkjet head is halted, the dissolved gas in the liquid inside the tank is removed, and the liquid in the tank is then supplied to the inkjet head.
However, when the saturated amount of dissolved gas in the ink varies with environmental changes (in particular, temperature changes) of the inkjet head and the ink supply system, then the differential (which corresponds to the gas dissolving capacity) between the saturated amount of dissolved gas and the actual amount of dissolved gas changes, accordingly. In other words, the tendency of the dissolved gas contained in the ink to be ejected from the inkjet head to form gas bubbles depends on variation in the ink temperature, and the like.
Therefore, even if the amount of dissolved gas in the ink inside the inkjet head is controlled by using a deaerator, or the like, in such a manner that the amount of dissolved gas in the ink inside the inkjet head does not exceed the prescribed value, there is a possibility that gas dissolved in the ink in the inkjet head might form gas bubbles in cases where the ink temperature rises after the inkjet printer starts operation. This leads to giving rise to loss of ejection pressure, which may cause ejection abnormalities, such as ejection failures, or the like.
Moreover, printing needs to be interrupted and the dissolved gas needs to be removed by using a deaerator, or the like, when the amount of dissolved gas is greater than the prescribed value. Therefore, printing cannot be carried out until the amount of dissolved gas becomes equal to or lower than the prescribed value, and hence wasteful waiting time arises.